Nanofluidics is defined as fluidic systems with channels in the nanometer range size, and has been applied in microfluidic systems allowing for DNA manipulation, protein separation and sample preconcentration. A majority of the current nanofluidic developments are intended for bioengineering and biotechnology applications.
Current practices for the detection of specific biomolecules can be divided in two categories: (a) the labeled techniques and (b) the label-free techniques.
Among the labeled techniques, the widely used are fluorescence, colorimetry, radioactivity, phosphorescence, bioluminescence and chemiluminescence. Functionalized magnetic beads can also be considered as labeling techniques. Their advantages are the sensitivity in comparison to label-free methods and the molecular recognition due to specific labeling.
Among the label-free techniques, the widely used are electrochemical biosensors, referring to amperometric, capacitive, conductometric or impedimetric sensors, which have the advantage of being rapid and inexpensive. They measure the change in electrical properties of electrode structures as biomolecules become entrapped or immobilized onto or near the electrode, but all these concepts lack molecular specific contrast, sensitivity and reliability.
Surface plasmon resonance (SPR) is also a label-free optical technique for monitoring biomolecular interactions occurring in very close vicinity of a transducer gold surface, and has lead to great potential for real-time studying surface-confined affinity interactions without rinsing out unreacted or excess reactants in sample solutions.
Enzyme linked immunosorbent assay (ELISA) is an important biochemical technique mainly used to detect the presence of antibodies and antigens, and thus is widely used as diagnostic tool in medicine and quality control check in various industries. ELISA analysis are however expensive, require large amounts of solution and a long time to obtain results.